This invention is directed to the adjustment as it relates to face-cutting apparatus for making and treating pellets of thermoplastic material.
Face-cutting apparatus of the type described is disclosed in U.S. Pat. No. 3,316,590. In such apparatus, the die plate means associated with a thermoplastic extruder device is cylindrically shaped and is provided with radially extending extrusion orifices through which heat-plastified material is extruded by reason of the operation of a rotating feed-screw which pressurizes the material upstream of the die plate means. The blade of a single-lead cutter has a cutting edge which is operatively associated with the downstream face of the die plate means, and which shears heat-plastified material extruded through the orifices into pellets. The cutter is enclosed to establish a chamber receiving circulating liquid or gaseous coolant which serves to improve the cutting-efficiency and to collect the pellets as they are formed.
The pellet thickness achieved with apparatus of the type described depends upon the rate of rotation of the cutter and the rate at which the plastic material is extruded. If the cutter speed is essentially constant, variations in pellet thickness can be attributed to changes in the rate of extrusion. Such rate is determined in large part by the viscosity of the thermoplastic material just upstream of the die plate means. As the viscosity increases, due to upstream temperature reduction, for example, less material is extruded per unit time, and the resultant pellets will be thinner than when the viscosity decreases. In many processes, variations in pellet thickness is not important. In processes where uniformity is necessary because of size considerations or because of a need to remove a uniform percentage of volatiles from all of the pellets, apparatus heretofore available has not proved to be successful. The primary object of the present invention, therefore is to provide face-cutting apparatus which can effect the high speed production of uniform pellets.